Re-consider access token lifespan

At the moment NSS defines a default 14-day token lifespan: https://github.com/solid/oidc-op/blob/main/src/AccessToken.js#L7
Why re-consider?

• a long life for NSS access tokens affects the entire Solid ecosystem. If another server (e.g. ESS, CSS) wants to support NSS access tokens, it needs to accept tokens with a very long life.
• Bearer tokens (which is what we're talking about) are global in nature for Solid. They are extremely powerful and so any exfiltration can have significant negative consequences (i.e. a user loses data to a malicious actor). Reducing the lifespan of a global access token reduces risk for everyone
• for access tokens (especially global access tokens) the industry standard is <= 1 hour. For access tokens that secure "sensitive" data, the standard is closer to 10 minutes or less

Suggestions:

1. Request a refresh token during the authorization code flow (this is part of OpenID Connect). Then, when the token is nearing expiry, exchange the refresh token for a new access token
2. Completely refresh the app, passing the user through the full authorization code flow (part of OIDC). There will still be a cookie available on the identity provider, so the user will, in all likelihood, be passed right through the redirect flow and end up where they started. There are patterns for maintaining state between the start and end of that flow

• If the cookie expired on the Identity Provider, then the user would need to re-enter credentials
• NSS uses cookies so we could exchange the access token with a cookie.
  Example: Gmail uses cookies. Cookies are easy to scope to a particular app, so there are no significant security issues.

まず src/AccessToken.js のデフォルトの14日間の有効期間から始め、その後、issue で説明されている authorization code flow、refresh-token option、Cookie の処理、OpenID Connect に関する考慮事項を確認します。実装前にセキュリティ設計を決定する必要があります。done には、トークンの有効期間に関する合意済みの戦略と、それが更新および再認証に与える影響を含める必要があります。